A recombinant classical swine fever virus stably expresses a marker gene

The gene coding for bacterial chloramphenicol acetyltransferase (CAT) was inserted in frame into the viral N-pro gene of the full-length cDNA clone pA187-1 of the classical swine fever virus (CSFV) strain Alfort/187. RNA transcribed in vitro from the resulting plasmid was transfected into SK-6 porcine kidney cells. Infectious progeny virus vA187-CAT recovered from transfected cells had growth characteristics indistinguishable from those of parental virus vA187-1. In cells infected with vA187-CAT the predicted fusion protein, CAT-N-pro, was detected, and it retained the enzymatic activities of both CAT and N-pro. The CAT gene remained stably inserted in the viral genome after 10 virus passages. Thus, marker virus vA187-CAT represents a useful tool for quantitative analysis of viral replication and gene expression.